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IP verification on email

Posted on 2004-09-20
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Last Modified: 2012-06-21
Hello,

I have an issue with some companies that are doing a reverse look up on email leaving my org.  If they can't find my external IP they will tag the email as SPAM.

How does this process work and what exactly are these reverse lookups looking for?

I send directly out to the internet from my exchange server which is in the inside network.

Thanks,.
Juan
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Question by:jibarra
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Expert Comment

by:Sembee
ID: 12105808
You know how DNS works?

Enter a name (www.domain.com) and the DNS system finds that www.domain.com is on the server with the IP address 10.10.10.10.

What reverse DNS does is lookup what is on 10.10.10.10.
Depending on how strict they are will depend on whether they are just looking for something on that address, or whether it matches what your server is announcing itself as.

Therefore if your server announces to the world as server1.domain.local but the IP address that it is coming from is mail.domain.com then that can cause problems.

You can use the tools at dnsstuff.com to see what the Internet thinks is your reverse lookup on your IP address.

How do you fix?
Your ISP needs to resolve the reverse DNS lookup, as they own the IP address. Ask them to put a reverse DNS on to your IP address.

To get Exchange to announce itself as the name that it is known as requires a change to the SMTP settings on Exchange. You haven't said which version of Exchange you are using, so I cannot really tell you where that is.

Does that help?

Simon.
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Author Comment

by:jibarra
ID: 12105973
Although not an expert, I know how DNS works.  I am using Exchange 2003 on windows server 20003.
Is it a good practice to allow this reverse look up as not all domains have this problem?
Thanks,
Juan
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Accepted Solution

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Sembee earned 125 total points
ID: 12106029
It is becoming a problem so I now do it for all sites that I setup. I see no reason not to.

AOL is probably the biggest use of reverse lookups - it is failing to send to AOL that is usually the indicator of a problem. Many of the US based cable ISPs are also starting to use them.

Sometimes even having a reverse DNS lookup in place will not help. Another common practise is to block by IP range. The IP ranges used for dial up and ADSL are well known and many ISPs don't believe that you should be running a server from those. In these cases it usually means that you need an SMTP connector to send email through the ISP's SMTP server.

Simon.
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